Variable Capacitor is one of the type of basic capacitors. Based on the capacitance, capacitors are classified under two categories. These are referred to as ‘Fixed Capacitors’ and the ‘Variable Capacitors’. The capacitors with the capacitance value are fixed are known as ‘Fixed Capacitors’. Similarly, the capacitors that are with varying amounts of capacitance are known as Variable Capacitors.
This type of capacitor has the capability of changing the values of its capacitance either “Electrically” or “Mechanically”. Instead of deciding the values during manufacturing like Fixed Capacitors, certain ranges of values are provided in Variable Capacitors. Based on the required values these capacitors are chosen. In most of the Tuning Circuits, this type of capacitor is preferred.
What is a Variable Capacitor?
- A capacitor whose capacitance can be varied based on the requirement to a certain range of values is defined as a Variable Capacitor.
- These types of capacitors consist of plates made of metals.
- Among these plates, one will be fixed while the other is movable.
- The range of the capacitance provided by these capacitors is from 10 picofarads to 500 picofarads.
- These capacitors can be interconnected with each other. This can be referred to as ‘Ganged Capacitors’.
- This combination is done in such a way that one shaft is sufficient for rotating the ends of the capacitors that are variable.
In this way, the variable capacitors can be defined. The symbol for this type of capacitor is simple. It consists of an arrow on it to represent that it is a variable one.
Variable Capacitor Symbol
Construction :
- The construction of this capacitor is possible by plates of metal in it.
- In this some of them are ‘Fixed Plates’ and the remaining is ‘Movable Plates’.
- Because of the rotation of the plates that are movable the area in between the Fixed and the plates that are movable also changes.
- Each type of capacitor in this has a different way of construction.
Working :
The working of the ‘Variable Capacitor’ is based on the type of design and the moving metal plate determines the value of the capacitance. In this article, we are about to discuss the most popular types of these capacitors. Let us discuss them in detail.
Variable Capacitor Types :
The most popularly used Variable Capacitors are
- Tuning Capacitors
- Trimmer Capacitors
The capacitance of these capacitors can be varied with the help of screwdrivers or by any other devices manually.
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Tuning Capacitors
- These capacitors are constructed with the help of a frame. It consists of a ‘Stator’ and a ‘Rotor’.
- The frame in this capacitor provides support to the capacitor made of mica and the ‘Stator’ present in it.
- With the help of the shaft, the rotor tends to rotate. While the stator is stationary.
- Once the plates of the movable rotor enter into the stationary stator. At this situation, the capacitance is considered to be at the maximum level.
- Otherwise, the value of the capacitance is considered to be minimum.
Tuning Capacitor
- The range of the values of capacitance provided by these capacitors is from certain ‘pico farads’ to ‘tens of picofarads’.
- In the receivers used in Radios which possess ‘LC circuits’ these types of capacitors are preferred.
- These types of capacitors are also known as “Tuning Condensers”.
That’s how the Tuning Capacitors works and utilized based on preferred requirements.
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Trimmer Capacitors
The capacitors that consist of screws on it so that one can change the value of capacitance are known as Trimmer Capacitors. These capacitors are adjusted with the capacitance such that it is fixed based on requirements with the help of ‘Screw Driver’.
- This type of capacitor consists of three ‘Leads’.
- Among those three leads, one is connected to the stationary part; the other lead is connected to the part that is responsible for the movement called rotary. The other lead is Common.
- The movement can be seen through the movable disc. It is in the shape of a semi-circle.
- The shape of the Trimmer Capacitor consists of the two plates that are parallel to each other. These are separated by the Dielectric.
- Based on the type of dielectric chosen these are classified as ‘Air Trimmer Capacitors’ and ‘Ceramic Trimmer Capacitors’.
Trimmer Capacitor
- Among two plates one of the plates is considered to be fixed and the other is considered to be in movement or movable.
- The Dielectric present in this capacitor is ‘Fixed’.
- The movable plate is moved in the opposite towards the area in between the fixed and the movable electrodes.
- In this way, the capacitance of the capacitor can be altered.
- The capacitance value and the area are proportional to each other.
- If the area between the electrodes tends to increase the value of capacitance increases.
and that’s how a Trimmer Capacitor works.
Variable Capacitor Uses
There are various applications of these Variable Capacitors. Some of them are listed as follows:
- In this capacitor, the type called Trimmer Capacitor can be easily used on the ‘Printed Circuit Board‘.
- These are preferred in the ‘Calibration’ of the equipment.
- These are used in the ‘Receivers’ of radio. Where the LC circuits are present.
The above are the most practical uses of the Variable Capacitors.
These are very flexible and efficient in terms of matching the values of impedance. The above-discussed capacitors are tuned mechanically which are widely used. Even there exists electronically type of Variable Capacitors. Which one of the Variable Capacitor you are familiar with? Know more about Film capacitor.